Triggered spark gap



June 7, 1949. w. G. MAYER 2,472,115

TRIGGERED SPARK GA]? T U m l8 '4 Filed June 25, 1943 F l G. 5.

RANSMITTER INVENTOR.

' WILLIAM G. MAYER M QD/Au flrrurw PULSER Patented June 7, 1949 UNITED STATES PATENT QFFI'CE Application June 25, 1943-, Serial N6; 492L232 solaii'ns. (01. 250-28) (Granted under the act of March 3, 1883], as amended April 30, 1928'; 370 O. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes; without the payment to iiie of any royalty thereon; N

This invention relates to spark gap modulators or keyers; and more particularly to such a spark gap in which the timing of the spark is controlled by means of a third, or triggering, electrode.

Stationary gaps have been used to modulate or key a pulse transmitter; but suffer fromthe disadvantage that the spark, and consequently the resulting pulse, is aperiodic. To provide periodicity it has been proposed to use a rotary spark gap, but it has been found that even with a rotary gap a slave sweep oscilloscope is neededbecause of an error of; say, 50 to 100 microseconds in the control. Moreover, there is the added complication and expense of a inotor and mechanical mounting for high speed rotation. v

The primary object of the present invention. is to generally improve spark gap modulators or keyers. A more particular object is to overcome the foregoing disadvantages and to provide a stationary spark gap in which the main pulse is very accurately controlled by a triggering pulse. A more detailed object is to provide a triggered spark gap in which there is practically no wear at the triggering electrode. Still further objects are to provide a triggered spark gap which is simple; cheap; readily adjustable; and useable over wide ranges of potential and pulse frequency.

To accomplish the foregoingand such other objects as will hereinafter appear, my invention consists in the spark gap elements, and their relation one to the other, ashereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by a drawing in which Figure 1 is a front elevation of a triggered spark gap embodyin features of my invention;

Figure 2 is a transverse section drawn to an enlarged scale taken approximately in the plane of the line 2-2 of Figure *1; v

Figure 3 is a plan view of the triggering electrode looking in the direction of the arrows 3-3 in Figure 2;

Figure 4 is a 'v'ertical'section through the lower electrode taken approximately in the plane of the line 44 of Figure'3;

Figure 5 is a schematic wiring diagram eX- planatory of a typical circuit usin the triggered sparl; gap.

Referring to the draw ng and more particularl y'to Figures 1 and 2; the fspark g'ap comprises main electrodes [2 aha I4, with a gap therebe- 1 tween; The aegt're es aie preferably eossaeu'y arranged; as shown; In-

ame, with a featlli' "or the preseiit iiiye'fiitioj" as insulation washer [6 su rouziq's the ictie'de i near the gap. The washer is pi'fera iiia'de of g ass or other ceramic'. A triggiiiig'elctrode [Bis positioned with its Working 'rid i'e'stihg' up'oii th washer l6 near the main eieaiedem J The complete structure is'prferably provided with means affordiiig'adjustnient of the spacing between the mainelctiodes; In the present case, the upper electrode I? is carried at the lower end of an adjusting serew go; which' is threadedly received in a stationary nut 22; A 24 0f insulating material carried at the pper end of screw 20; facilitates adjustinntof the main sap; It is desirable to mov es meansto' lockthe adjustment and; in the present case; the nut 22 is a block of metal split at and provided with a clamping screw 28; Block 22 is carried on a cross-bar 30; supporteiiby insulation pedestals 32. It will be understood that the solid end of b1o'c'k'22 is brazedo'r otherwise secured tti crossbar so; While at least one or the split sides of the block is left nee to perxiiit lanfiping movement under the action er elaiiipiiig screw 28.

.The spacing "betl'lv'ecfi the" triggering electrode l8 and the cooperating inairi netibde Misalso preferably made adjustable. I Referring to Figures 2 and Sit will be seeii'that triggering electrode is is carried on an 'itisiilatitifi pedestal 34, and is axes in positlonby 'mearisflbf a 36; Screw it passes through asidt 38 iii electrode l8; and this slot prmitsinoyih'ent' btthetriggerin electrodetoward or away fldni the ma n electrode;-

It will be notedthatj the mair'i'electrods I2 and M are"substantiallydifferrit in" diameter. The large diameter eldtrode i2 is used as a cathode, thereby reducingthe rate of consumption of the same. As the cathode is consumed, the main gap may be readjusted to desired size by means of the adjusting Screw" 20 'afid' 'kriiib '2 4; b'iviously referred to. Thesmaller diameter electrode M is used as an, anode-Kendall; is this electrode that is surrounded by-t'he ggla ss washer {6. The triggering electrode ma be a" flat strip of metal, as show n,- and itsimier'orworking end is preferably curved on; an arc concentric with the anode 56. Ihave found that atrisgering electrode which only partly'surrounds" the main electrode is superior to the use of a ring" Wholly surrounding themain electrode. I-Iowever it is not necessary 9 edi pswee re whe l-t t electrode id the comparatively srn ll fish-tail shapeshown in Figure Bbf thi drawing In {act a ringalmostvbut not completely Surrounding the main electrode is 3 satisfactory, although not as good as the illustrated fish-tail shape. I have found that the ring should be at least split or cut open at one point, and that it is not desirable to use a completely closed ring.

The triggering electrode is preferably held in contact with the glass washer. I have found that the presence of the glass washer, with the triggering electrode resting thereon, makes considerable difference in the successful operation of the gap, although the exact reasons for the improvement are still obscure and must be deemed an empirical discovery.

The electrodes are all preferably made of a suitable high temperature metal. Tungsten is very satisfactory for the main electrodes l2 and I4, and

molybdenum is most satisfactory for the triggering electrode I8, but tantalum or tungsten may also be used for the triggering electrode. Despite the use of such high temperature metals, there is a tendency toward volatilization and consumption of the electrode material. This tendency may be inhibited by holding down the temperature of the electrodes. With this object in View, the main electrode i2 is socketed in a larger body of 2. preferably heat-conductive and electricallyconductive metal, such as copper or aluminum. To provide maximum cooling surface, the body 40 is preferably cut to form a series of relatively thin cooling fins 42. The body 40 is secured to the lower end of the adjusting screw 20, and the cathode I2 is preferably detachably received in body 40, it being releasably held by suitable means, such as set screw 44, so that it may be replaced when consumed.

The anode I4 is similarly removably socketed in a larger body of metal 46, which is also preferably heat-conductive and electrically-conductive (typically copper or aluminum), and which may be cut to provide cooling fins 68. This body may be formed integrally at the upper end of a post 50, the lower end of which is secured to the insulation base 52 of the spark gap. The electrode [4 is held by a set screw 54, as is best shown in Figure 4, and in this case the set screw serves the additional function of affording axial adjutment of the position of electrode [4. Inasmuch as this electrode is used as the anode, there is substantially no consumption of the same, but axial ad- J'ustment is desirable in order to make it possible a to adjust the axial distance between the working end of the electrode I4 and the working end of the triggering electrode 18. From another viewpoint, it may be said that the adjustment is intended to control the spacing of the glass washer Hi from I the end of electrode Hi, this spacing being important to secure best operation. Inasmuch as the triggering electrode is kept in contact with the glass washer, both adjustments amount to the same thing.

In the particular structure here shown, the electrode I4 is carried in an intermediate holder 56 (see Fig. 4), which in turn is set into the main holder 46, and is there locked in position by a set screw 58. However, it is equally satisfactory to make the entire holder out of one piece of metal, that is, to make the parts 46 and 56 integral.

No special means is here shown to cool the triggering electrode [8, other than the formation of this electrode at the end of a relatively wide plate of metal, thus providing a substantial cooling surface. In any case, cooling of the triggering electrode is not very important with my improvement, because the triggering electrode runs cool, and is only very slowly, if at all, consumed. Under .4 optimum adjustment the gap will run with no visible spark between the triggering electrode and the cooperating main electrode, the only visible spark being the main spark between the main electrodes.

External connection to the upper electrode is made by means of a binding post 60 (see Figure 1), carried on the top of cross-bar 30. Connection to the lower electrode is made by means of a binding post 62 mounted on metal post 50. Connection to the triggering electrode l8 may be made by means of the screw 36 previously referred to, or by means of another binding post, not shown.

The upper end of the lower electrode or anode is preferably rounded, as shown in the drawing. The lower end of the upper electrode or cathode may be left square, or may be rounded as shown, if desired. The shape is not too important because after long wear the upper electrode becomes concave because of consumption of electrode material.

For purposes of illustration, but not in limitation of the invention, one example of a circuit using the triggered spark gap is shown in Figure 5. Referring to that figure, high voltage D. C. may be supplied at 10, and is used to charge a relatively large storage condenser 12. A choke M in series with the D.-C. supply serves the dual function of boosting the available charging potential and also of insuring termination of the spark when the condenser discharges. The available potential is selected to be high, but not high enough to break down the main spark gap. The triggering electrode i8 is supplied with a control pulse from a suitable pulse generator 16. This potential is high, but only a fraction of that available for the main gap l2-l4. The pulse provided by breakdown of the main gap is used to modulate a transmitter 18. The circuit of Figure 5 is primarily a test circuit. For actual transmission purposes, the condenser 12 and choke may be replaced with an artificial line or a network of limited impedance to shape or square the pulse. If desired, the connection between the artificial line and the transmitter may be made through a so-called pulse-transformer, that is, a transformer designed to successfully transmit a square pulse.

With the present spark gap it has been found that the control pulse controls the accuracy of the main pulse (that is, so-called jitter is held down) to within a, few one-hundredths of a microsecond. Such gaps have already been run and are still running on a very long life test at 14,000 volts (including the voltage-doubling action of the choke) with a 1 microsecond pulse, at a rate of 200 pulses per second.

There is practically no visible spark between the triggering electrode and the main electrode, which probably explains the negligible wear of the triggering electrode. It produces an ionization or slight corona which immediately leads to breakdown of the main gap.

In a particular spark gap which I used with considerable success, the upper electrode was a A" tungsten rod used as a cathode; the lower electrode was a 1 s tungsten rod used as an anode; the triggering electrode was a molybdenum plate 0.02 inch thick; and the glass washer was in diameter and thick. The main gap was approximately in length, and the trigger gap was approximately 1%" in length. The anode projected above the glass washer A. As an example of the control effect, it may be stated that the gap may be made to break down at 8,500

volts initial potential (not counting the double action of the choke), although it would require 18,000 volts to break down the same gap when not using the triggering electrode. It should be understood that these specific dimensions are given by way of example, and not in limitation of the invention.

It is believed that the construction, operation and method of using my improved spark gap, as well as the advantages thereof, will be apparent from the foregoing detailed description. The gap is simple; cheap; readily adjustable; and usable over wide ranges of potential and pulse frequency. There is practically no wear of the triggering electrode, and any wear of the cathode is readily made up by adjustment. There is practically no jitter, for the accuracy of control is kept to within a few one-hundredths of a micro-second. How the glass washer influences the operation of the gap is still obscure, but there is no question about the benefit of this improvement.

It will be apparent that while I have shown and described my invention in a preferred form, changes and modifications may be made in the structure disclosed without departing from the spirit of the invention as sought to be described in the following claims. In the claims I have for convenience used the term "glass but this is not intended to exclude the use of other equivalent ceramics, and. other high temperature insulation, such as Mycalex and mica.

Iclaim:

1. A triggered spark gap operable in air comprising main electrodes with a gap therebetween, a ceramic washer surrounding one of said electrodes near said gap, and a triggering electrode having its working end adjacent the aforesaid ceramic washer near the electrode carrying said ceramic washer, said working end being substantially an arc of less than 360 substantially coaxial with said last mentioned electrode.

2. A triggered spark gap operable in air comprising coaxially arranged first and second main electrodes disposed end to end with a gap therebetween, a glass washer surrounding said first main electrode near said gap, and a fiat metal triggering electrode positioned transversely of the main electrodes and having its working end adjacent the aforesaid glass washer and partially but not wholly surrounding said first main electrode. L H

3. A triggered spark gap operable in air comprising two main electrodes with a gap therebetween and a triggering electrode having its working end adjacent one of the main electrodes and spaced from the spark path between said main electrodes, a source of high-voltage across said main electrodes, which source alone is of insufficient magnitude to break down the gap and cause spark discharge between said main electrodes, a source of voltage between the triggering electrode and the adjacent main electrode of sufficient magnitude to cause corona but not spark discharge therebetween, so as to thereby trigger a spark discharge between the main electrodes.

4. A triggered spark gap as defined in claim 3 wherein the triggering electrode is disposed substantially perpendicularly to the adjacent main electrode and said triggering electrode includes a working end which is of substantially arcuate configuration of less than 360 and is substantially coaxially positioned relative to the said adjacent main electrode.

5. A triggered spark gap as defined in claim 3 which includes a washer of ceramic material positioned about the main electrode adjacent to the triggering electrode and which washer is proximate to the working end of the said triggering electrode.

WILLIAM G. MAYER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 802,850 De Forest Oct. 24, 1905 976,778 Brown Nov. 22, 1910 1,424,141 Fuller July 25, 1922 1,623,982 Smith Apr. 12, 1927 1,739,118 Bidwell Dec. 10, 1929 1,747,050 Charlton Feb. 11, 1930 1,760,524 Rentschler May 27, 1930 1,760,525 Rentschler May 27, 1930 1,789,626 Kendry Jan. 20, 1931 1,897,471 Foulke Feb. 14, 1933 1,970,525 Lyons Aug. 14, 1934 2,074,930 Marx Mar. 23, 1937 2,405,069 Tonks July 30, 1946 

